High voltage rectifier using low voltage CMOS process transistors

ABSTRACT

A high voltage full wave rectifier circuit having complementary serially connected low voltage MOSFET stacks provides high voltage rectifier capability. The MOSFET stacks are coupled to a pair of cross coupled MOSFETs that provide a full wave rectified output voltage. The state of the MOSFETs in the MOSFET stacks is controlled by resistors coupled between the rectifier output and a time varying input signal. The resistance values of the resistors are selected to maintain operation of the stacked MOSFETs below their breakdown voltages. A pair of diodes is connected between ground and the MOSFET stacks. A plurality of diode connected MOSFETs are connected between the rectifier output and the resistors to establish bias voltages on the gates of the MOSFETs in the MOSFET stacks to control operation of the rectifier during input voltage cycles. A voltage doubler circuit is also described where low voltage MOSFETs are utilized in a novel configuration to provide high voltage doubling capability.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35. U.S.C. 119(e) ofU.S. Provisional Application No. 61/332,475, filed on May 7, 2010, whichis incorporated herein by reference in its entirety.

FIELD

The disclosure relates generally to electronic integrated circuits. Inparticular, it relates to high voltage full wave rectifier and voltagedoubler circuits utilizing an exemplary 0.18 um CMOS process fortransistors arranged in series circuit configuration to facilitate usageof low voltage transistors in high voltage applications.

BACKGROUND

Implantable biomedical devices have been developed for differentapplications such as retinal prosthesis, cochlear implant, and armrehabilitation.

As an example, “A 232-channel epiretinal stimulator ASIC,” by M.Ortmanns et al., IEEE Journal of Solid-State Circuits, Vol. 42, pp.2946-2959, December 2007, which is incorporated herein by reference inits entirety, describes implantable biomedical devices developed forretinal prosthesis. Other examples include: “A 32-Site 4-ChannelCochlear Electrode Array,” by P. Bhatti et al., ISSCC Dig. Tech. Papers,pp. 50-51, February 2006, which is incorporated herein by reference inits entirety, describes implantable biomedical devices developed forcochlear implants and “A Biomedical Implantable FES Battery-PoweredMicro-Stimulator,” by E. Matei et al., Proc. IEEE 2008 CICC, pp.317-324, September 2008, which is incorporated herein by reference inits entirety, describes implantable biomedical devices developed for armrehabilitation.

Implantable biomedical devices are usually powered by inductive couplingdirectly from a radio frequency (RF) field or from a rechargeablebattery that is recharged by means of inductive coupling with anexternal RF field.

FIG. 1 shows an exemplary implementation of an inductively poweredimplantable medical device (100) used in both the case of implantablebiomedical devices powered by inductive coupling from an RF fielddirectly as well as from a rechargeable battery managed by a batterymanagement unit. As shown in FIG. 1, a primary voltage V₁ (105) from afirst coil L_(S) (110) induces a voltage V₂ (115) in a second coil L(120). More specifically, the coil L (120) located inside theimplantable device (100) receives power by means of magnetic couplingfrom an external magnetic field generator (125). In general, overallpower consumption for most implantable biomedical devices (100) isrelatively low, usually not exceeding tens of milliwatts.

The induced voltage V₂ (115) is rectified and converted to a DC voltageV_(DC) (130) by a rectifier (135). The DC voltage V_(DC) (130) is usedfor powering circuits in the implantable device (100) directly or forrecharging a battery in the implantable device (100). Peak to peakinduced voltage V₂ (115), denoted as V_(2Pk-Pk), depends on a number offactors such as:

-   -   (a) design of coil L_(S) (110) and coil L (120) including the        turns ratio,    -   (b) equivalent load seen by the circuit comprising coil L (115)        and a tuning capacitor C (140),    -   (c) magnitude of the external magnetic field provided by        generator (125), and    -   (d) distance between and orientation of coil L_(S) (110) and        coil L (120).        The peak to peak voltage V_(2Pk-Pk) of the induced voltage V₂        (115) can range from a few volts to around 20 V.

In the following figures, NMOSs and PMOSs will be used in exemplaryimplementations of circuit devices. The NMOS has a threshold voltagedenoted as V_(TN) and the PMOS has a threshold voltage denoted asV_(TP). A typical value for the threshold voltages is 0.5 volts for anexemplary 0.18 um CMOS process.

FIGS. 2A and 2B show two exemplary implementations of conventional CMOSfull wave rectifier circuits and it is instructive to discuss operationof these circuits in detail in order to gain a better understanding ofthe novel advancement the current invention provides over the presentstate of the art.

FIG. 2A shows a first implementation of a conventional CMOS full waverectifier circuit (200). The implementation in FIG. 2A comprises a firstNMOS field effect transistor (FET) M₁ (205), a second NMOS FET M₂ (210),a first diode connected PMOS FET M₃ (215), and a second diode connectedPMOS FET M₄ (220). A diode connected FET is referred to in aconfiguration when a FET gate and drain are connected together so thatthe FET functions as a diode. The drain of the first NMOS FET M₁ (205)is connected to the source of the first PMOS FET M₃ (215) and the drainof the second NMOS FET M₂ (210) is connected to the source of the secondPMOS FET M₄ (220). The two NMOS FETs M₁ (205) and M₂ (210) are connectedtogether in what is referred to as a cross coupled arrangement. Inparticular, the gate of the first NMOS FET M₁ (205) is connected to thedrain of the second NMOS FET M₂ (210) and the gate of the second NMOSFET M₂ (210) is connected to the drain of the first NMOS FET M₁ (205).

An induced voltage V₂ (202) is a difference between voltage V_(R1) (225)appearing at node N_(R1) (226) and voltage V_(R2) (230) appearing atnode N_(R2) (231), namely V₂=V_(R1)−V_(R2). When NMOS FET M₁ (205) isconducting (or “ON”), node N_(R1) (226) is connected to ground (235).Similarly, when NMOS FET M₂ (210) is conducting, node N_(R2) (231) isconnected to ground (235). Voltages 225 or 230, at nodes 226 or 231respectively, are applied to output node N_(OUT) (241) by means of diodeconnected PMOS FET (215 or 220) and supply an output current I_(OUT)(242) to a load circuit (not shown).

Operation of the circuit of FIG. 2A is as follows: consider a case whenthe induced voltage V₂ (202) is at a peak value V_(2P) with the voltageV_(R1) (225) at its maximum value and the voltage V_(R2) (230) at itsminimum value.

The second NMOS FET M₂ (210) has the voltage V_(R2) (230) applied to itsdrain, the voltage V_(R1) (225) applied to its gate, and the groundterminal (235) tied to its source. The second NMOS FET M₂ (210) operatesin the triode mode since V_(GS2)=V_(R1)>V_(TN) andV_(GD2)=V_(R1)−V_(R2)>V_(TN), where V_(GS2) is the gate-to-sourcevoltage of the NMOS FET M₂ (205) and V_(GD2) is the gate to drainvoltage of the NMOS FET M₂ (210) The second NMOS FET M₂ (210) is turnedon (conductive) and node N_(R2) (231) is tied to the ground terminal(235). Therefore, current flows from node N_(R2) (231) to the groundterminal (235).

The first NMOS FET M₁ (205) has the voltage V_(R1) (225) applied to itsdrain, the voltage V_(R2) (230) applied to its gate, and the groundterminal (235) tied to its source. The first NMOS FET M₁ (205) operatesin cutoff mode because V_(GS1)=V_(R2)<V_(TN), where V_(GS1) is thegate-to-source voltage of the NMOS FET M₁ (205). Therefore, nosignificant current flows through the NMOS FET M₁ (205).

The voltage V_(R1) (225) appearing at N_(R1) (226) is sufficiently largeso as to turn on the diode connected PMOS FET M₃ (215). The node N_(R1)(226) is tied to output node N_(OUT) (241), and thus the voltage V_(R1)(225) minus a voltage drop typically in the range of 0.5 to 1.0 voltsdue to the diode connected PMOS FET M₃ (215) is applied to the loadcircuit (not shown). The voltage V_(R1) (225) minus a voltage drop dueto the diode connected PMOS FET M₃ (215) is denoted as an output voltageV_(DD) (240) in FIG. 2A.

A similar case exists when the voltage V_(R2) (230) is at a maximumvalue and the voltage V_(R1) (225) is at a minimum value. The first NMOSFET M₁ (205) operates in a triode mode and thus node N_(R1) (226) istied to the ground terminal (235). The second NMOS FET M₂ (210) operatesin cutoff mode. The voltage V_(R2) (230) turns on the diode connectedPMOS FET M₄ (220), and thus the voltage V_(R2) (230) minus a voltagedrop due to the diode connected PMOS FET M₄ (220) is applied to the loadcircuit (not shown). In this case, the output voltage V_(DD) (240) inFIG. 2A is the voltage V_(R2) (230) minus a voltage drop due to thediode connected PMOS FET M₄ (220).

A technical paper entitled “Fully Integrated Wideband High-CurrentRectifiers for Inductively Powered Devices,” by M. Ghovanloo and K.Najafi, IEEE Journal of Solid-State Circuits, Vol. 39, No. 11, pp.1976-1984, November 2004, which is incorporated herein by reference inits entirety, proposes a technique to prevent a latch-up condition dueto parasitic bipolar transistors associated with the PMOS FETs (215,220).

FIG. 2B shows a second implementation (250) of a conventional CMOS fullwave rectifier. The implementation in FIG. 2B comprises a first PMOS FETM₁ (255), a second PMOS FET M₂ (260) in a cross coupled arrangement, afirst diode D_(NS1) (265), and a second diode D_(NS2) (270). Inparticular, the gate of the first PMOS FET M₁ (255) is connected to thedrain of the second PMOS FET M₂ (260) and the gate of the second PMOSFET M₂ (260) is connected to the drain of the first PMOS FET M₁ (255).The bulk terminals of the PMOS FETs (255, 260) are connected to theoutput voltage V_(DD) (240).

The diodes D_(NS1) (265) and D_(NS2) (270) connect either node N_(R1)(226), at which voltage V_(R1) (225) appears, or node N_(R2) (231), atwhich voltage V_(R2) (230) appears, to the ground terminal (235). Thevoltage 225 or 230 is applied to the load circuit (not shown) andsupplies the output current I_(OUT) (242) through the corresponding PMOSFETs 255 or 260.

The following analysis is similar to that given in relation to FIG. 2A.The first diode D_(NS1) (265) has the voltage V_(R1) (225) applied toits cathode and the ground terminal (235) tied to its anode. The seconddiode D_(NS2) (270) has the voltage V_(R2) (230) applied to its cathodeand the ground terminal (235) tied to its anode.

Consider a case when the induced voltage V₂ (202) is at the peak valueV_(2P) with the voltage V_(R1) (225) at its maximum value and thevoltage V_(R2) (230) at its minimum value. Diode D_(NS1) (265) isreverse biased since its cathode is positive relative to its anode. Thediode D_(NS2) (270) is forward biased since its cathode is negativerelative to its anode. The node N_(R2) (231) is thus tied to the groundterminal (235). Consequently, current flows from node N_(R2) (231) tothe ground terminal (235) whereas no significant current flows from nodeN_(R1) (226) to the ground terminal (235).

The second PMOS FET M₂ (260) has the voltage V_(R2) (230) applied to itsdrain, the voltage V_(R1) (225) applied to its gate, and the output nodeN_(OUT) (241) tied to its source. The second PMOS FET M₂ (260) operatesin cutoff mode because V_(GS2)=V_(R1)−V_(DD)>V_(TP), where V_(GS2) isthe gate-to-source voltage of the PMOS FET M₂ (260). Consequently, nocurrent flows from the second node N_(R2) (231) to the output nodeN_(OUT) (241).

The first PMOS FET M₁ (255) has the voltage V_(R1) (225) applied to itsdrain, the voltage V_(R2) (230) applied to its gate, and the output nodeN_(OUT) (241) tied to its source. The first PMOS FET M₁ (255) operatesin triode mode because V_(GS1)=V_(R2)−V_(DD)<V_(TP) andV_(DG1)=V_(R1)−V_(R2)>|V_(TP)|, where V_(GS1) is the gate-to-sourcevoltage of the PMOS M₁ (255) and V_(DG1) is the drain-to-gate voltage ofthe PMOS FET M₁ (255). Consequently, the first PMOS FET M₁ (255) isturned on and node N_(R1) (231) is tied to output node N_(OUT) (241). Asa result, current flows from node N_(R1) (226) through the first PMOSFET M₁ (255) to the output node N_(OUT) (241). The voltage V_(R1) (225)minus a small voltage drop due to the diode D_(NS2) (270) is applied tothe load circuit (not shown). This small voltage drop is typically inthe range of tens of mV and can be neglected typically for a largewidth-length ratio for the PMOS FET M₁ (255). The voltage V_(R1) (225)minus a voltage drop due to the diode D_(NS1) (265) is denoted as theoutput voltage V_(DD) (240) in FIG. 2B.

A similar case exists when the voltage V_(R2) (230) is at a maximumvalue and the voltage V_(R1) (225) is at a minimum value. The firstdiode D_(NS1) (265) is forward biased and thus ties the first nodeN_(R1) (226) to the ground terminal (235) and the second diode D_(NS2)(270) is reverse biased. The voltage V_(R2) (230) turns on the PMOS FETM₂ (260), and thus the voltage V_(R2) (230) minus a voltage drop due tothe PMOS FET M₂ (260) is applied to the load circuit (not shown). Inthis case, the output voltage V_(DD) (240) in FIG. 2A is the voltageV_(R2) (230) minus a voltage drop due to the PMOS FET M₂ (260).

For both conventional rectifiers shown in FIGS. 2A and 2B, the voltagesacross different terminals of the PMOS FETs and/or NMOS FETs willtypically see the full swing of the induced voltage. Therefore, thebreakdown voltages or the voltage limits of these FETs (typically in therange of ˜3.6V for a conventional 0.18 μm CMOS process) have to behigher than the peak induced voltage such that stress conditions willnot occur on these FETs. As a result, an induced voltage with large peakvalue (>˜3.6V) cannot be applied on these conventional rectifiers.

SUMMARY

To address the shortcomings and deficiencies of the current state of theart, the present invention discloses a high voltage full wave rectifiercircuit having complementary serially connected low voltage MOSFETstacks to provide high voltage rectifier capability. In particular, theMOSFET stacks are coupled to a pair of cross coupled MOSFETs thatprovide a full wave rectified output voltage. The state of the MOSFETsin the MOSFET stacks is controlled by means of a plurality of seriallyconnected resistors coupled between the rectifier output and the timevarying input signal. A pair of diodes is connected between ground andthe MOSFET stacks. A plurality of diode connected MOSFETs are connectedbetween the rectifier output and the resistors to establish biasvoltages on the gates of the MOSFETs in the MOSFET stacks to controloperation of the rectifier during input voltage cycles.

A voltage doubler circuit is also described where low voltage MOSFETsare utilized in a novel configuration to provide high voltage doublingcapability.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent disclosure and, together with the description of exampleembodiments, serve to explain the principles and implementations of thedisclosure.

FIG. 1 shows an exemplary implementation of an inductively powereddevice.

FIGS. 2A and 2B show exemplary implementations of conventional CMOS fullwave rectifiers. FIG. 2A shows an exemplary implementation of aconventional CMOS full wave rectifier comprising cross coupled NMOSs andPMOSs used as diodes. FIG. 2B shows an exemplary implementation of aconventional CMOS full wave rectifier comprising cross coupled PMOSs anddiodes.

FIG. 3 shows an exemplary embodiment of a high voltage full waverectifier according to the present disclosure.

FIG. 4 shows voltage waveforms for the high voltage full wave rectifiershown in FIG. 3.

FIG. 5 shows an exemplary embodiment of a high voltage (HV) voltagedoubler.

FIG. 6 shows voltage waveforms for the HV voltage doubler shown in FIG.5.

FIG. 7 shows an exemplary embodiment of a comparator.

DETAILED DESCRIPTION

The maximum voltage limit across exemplary 3.3 V transistor terminals,including the bulk terminal, is usually around 3.6 V. Nevertheless,breakdown voltages for different well diodes in a process utilizingDNWell/p-substrate diodes and NWell/p-substrate diodes are usuallyhigher. The breakdown voltages of the diodes determine the maximum inputvoltage for various devices, including an exemplary embodiment of a highvoltage full wave rectifier that is shown in FIG. 3 and an exemplaryembodiment of a HV voltage doubler that is shown in FIG. 5. For anexemplary 0.18 μm CMOS process, the diodes utilized in the processgenerally have breakdown voltages higher than 14 V.

Some applications require an induced voltage V₂ (115), shown in FIG. 1,with a high peak value V_(2P). As an example of such an application,with reference to the implantable device (100) in FIG. 1, stimulation ofnerve tissues using current pulses is performed using a DC voltageV_(DC) (130). The DC voltage V_(DC) (130) is at a high value in order toaccommodate different stimulation current pulse amplitudes and tissueimpedances. The DC voltage V_(DC) (130) is generally obtained from theinduced voltage V₂ (115) directly after rectification and conversion bythe rectifier (135), without any additional DC to DC converters.

Continued reference is made to the example of stimulation of nervetissues. Since high values are generally desired for the DC voltageV_(DC) (130) in such an application, integrated circuit (IC) processesused for this application is adapted to withstand high voltages. Sincethe implantable device (100) further comprises other circuits forcontrol, signal processing, and wireless communication, a two-chipsolution comprises one high voltage IC used for nerve tissue stimulationand one low voltage IC used for the circuit functions of controlling,processing, and communicating. However, the two-chip solution increasescomplexity in assembling the implantable device (100) due to the smallsize of many implantable devices (100).

Alternatively, IC processes providing both low voltage and high voltagecapabilities on the same chip can be used. However, choices for such anIC are limited and the low-voltage devices in such a process may notperform as well as the devices available in advanced CMOS processes. Asa result, some advantages available from advanced CMOS processes such ashigh logic density and low power consumption may be sacrificed for ICprocesses that provide both low voltage and high voltage capabilities onthe same chip. Therefore, it would be advantageous if the high voltagecircuits can be implemented using conventional low-voltage CMOSprocesses.

The present disclosure describes a high voltage full wave rectifier anda high voltage (HV) voltage doubler that can uses conventionallow-voltage CMOS devices. Both the high voltage full wave rectifier andthe HV voltage doubler achieve high voltage operation by stacking anumber of transistors typically NMOS and PMOS field effect transistorsthat are normally used in low voltage applications. In this contextstacking refers to connecting a plurality of transistors in seriescircuit arrangement wherein for example, the drain of the firsttransistor in the series is connected to the source of the secondtransistor in the series and the drain of the second transistor isconnected to the source of the third transistor in the series, and soon. Moreover, it is to be understood that, although the exampleembodiment of the high voltage full wave rectifier discussed hereinrelies on the use of PMOS devices, NMOS devices may also be used takinginto account the appropriate voltage polarity considerations known andappreciated by those skilled in the art. Furthermore, it is to beunderstood that with reference to components or devices that are“coupled” to other components, devices, voltage and current sources andground, etc. The term coupled includes the instance when the coupling is“direct” meaning that no other components are involved in the path fromthe subject device or component to its defined terminus and the instancewhen the coupling is “indirect” meaning that other devices or componentsmay lie in the path from the subject device or component to its definedterminus. Use of the high voltage full wave rectifier and the HV voltagedoubler in high voltage circuits allow integration of the high voltagecircuits with other low-voltage analog/RF circuits and digital circuitsin the same advanced process.

High Voltage Full Wave Rectifier Design

FIG. 3 shows an embodiment of a high voltage full wave rectifier (300)in accordance with the present disclosure. In the embodiment shown inFIG. 3, as already shown in FIG. 2B, the high voltage full waverectifier (300) comprises PMOS FET M₁₀ (305), PMOS FET M₂₀ (310), diodeD_(NS1) (315), and diode D_(NS2) (320). In the present embodiment, thediodes (315, 320) are NWell/p-substrate diodes. It is to be noted thatthe terms PMOS FET and NMOS FET and FET may be used interchangeably. Asshould be understood, the four components (305, 310, 315, 320) providethe overall rectification function of rectifier (300). A filtercapacitor C₃ (396) is connected between output node N_(OUT) (390) andground for output signal smoothing.

The embodiment shown in FIG. 3 however comprises additional componentsthat provide high voltage operation. In particular, the high voltagerectifier (300) further comprises a first PMOS FET stack (325)comprising (N) PMOS FETs M₁₁ (327) through M_(1N) (328) and a secondPMOS FET stack (330) comprising (N) PMOS FETs M₂₁ (332) through M_(2N)(333). As is shown in FIG. 3, the drain of the last PMOS FET M_(1N)(328) in the first PMOS FET stack (325) is connected to the cathode ofdiode D_(NS1) (315) and the drain of the last PMOS FET M_(2N) (333) inthe second PMOS stack (330) is connected to the cathode of diode D_(NS2)(320). Although three FETs are shown in respective FET stacks (325) and(330), other numbers of FETs may be used at the discretion of thedesigner depending upon the operating voltage range of the rectifier.

Additionally, with continued reference to FIG. 3, the HV rectifier (300)further comprises a first resistor ladder (340) comprising N resistorsR₁₁ through R_(1N) (343) connected to the gates of the respective FETsin the first FET stack (325) and a second resistor ladder (345)comprising N resistors R₂₁ through R_(2N) (348) connected to the gatesof the respective FETs in the second FET stack (330). The last resistorR_(1N) (343) in the first resistor ladder (340) is connected to a diodeconnected bipolar junction transistor (BJT) D₁ (350). The diodeconnected BJT D₁ (350) is connected to diode D_(NS1) (315). A lastresistor R_(2N) (348) in the second resistor ladder (345) is connectedin series circuit arrangement to a diode connected BJT D₂ (355). Thediode connected BJT D₂ (355) is connected to diode D_(NS2) (320). Theterm “diode connected” in the case of a bipolar transistor is used todenote the instance when the base of the transistor is connecteddirectly to the collector such that the transistor now functions as adiode. In a similar manner, the term “diode connected” refers to a FETwhen its gate is connected directly to its drain so that the FETfunctions as a diode.

The HV rectifier (300) further comprises a diode connected PMOS FETM_(B1) (360), a diode connected PMOS FET M_(B2) (362), and a diodeconnected PMOS FET M_(B3) (364). The diode connected PMOS FET M_(B1)(360) is connected to an output node N_(OUT) (390). The diode connectedPMOS FET M_(B3) (364) is connected in series circuit arrangement to thegate of PMOS FET M₁₁ (327) in the first FET stack (325), the gate ofPMOS FET M₂₁ (332) in the second FET stack (330), and the resistors R₁₁and R₂₁ of the respective resistor ladders (340, 345). The PMOS FETsM_(B1) (360) to M_(B3) (364) and resistor ladder (340) comprising Nresistors R₁₁ through R_(1N) (343) and resistor ladder (345) comprisingN resistors R₂₁ through R_(2N) (348) establishes a bias voltage at nodeA (373) equal to V_(DD) minus the voltage drop across the PMOS FETsM_(B1) (360) to M_(B3) (364). The resistance values for the resistors inresistor ladder (340) are selected to ensure that each of thecorresponding FETs in FET stack (325) have equal voltage drops acrosstheir respective source to drain terminals and that all of the FETs inFET stack (325) are operating below their breakdown voltages. Similarly,the resistance values for the resistors in resistor ladder (345) areselected to ensure that each of the corresponding FETs in FET stack(330) have equal voltage drops across their respective source to drainterminals and that all of the FETs in FET stack (330) are operatingbelow their breakdown voltages.

The bulk terminals of all the PMOS FETs are connected to theircorresponding source terminals so that the voltage across the drain andsource terminals of all the PMOS FETs will not exceed the transistoroperating voltage limits.

The following discussion of the operation of the HV rectifier (300)makes reference to both FIGS. 3 and 4. FIG. 4 shows voltage waveformsfor the high voltage full wave rectifier (300) shown in FIG. 3 under noload conditions. In particular, FIG. 4 shows, as a function of time, aninduced voltage V₂ (370), a voltage V_(R1) (375), a voltage V_(R2)(380), and an output voltage V_(DD) (395), also shown in FIG. 3.Specifically, time designations referred to as a first case a (400),second case b (405), and third case c (410) will be described in detail.

Case a: V_(R1) at maximum, V_(R2) at minimum

For the first case a (400) where the induced voltage V₂ (370) is at apositive peak value V_(2P) (370 a). Specifically, the voltage V_(R1)(375) is at a maximum value V_(R1-max) (375 a) and V_(R2) (380) is at aminimum value V_(R2-min) (380 a).

For simplicity, assume that the diode connected PMOS FETs M_(B1) (360),M_(B2) (362), and M_(B3) (364) have the same width-to-length ratios andthe same source-to-gate voltage, denoted as V_(SGB). In this simplifiedcase, an intermediate voltage V₁ (372) at a first intermediate node A(373) is V₁=V_(DD)−3V_(SGB).

The diode connected BJT D₁ (350) is forward biased whenV_(R1)<V₁−V_(D1), where V_(D1) is the diode voltage drop of the BJT D₁(350). However, in case a (400), the maximum value V_(R1-max) (375 a) ofV_(R1) (375) causes the diode connected BJT D₁ (350) to be reversebiased and consequently, no significant current flows through the firstresistor ladder (340). As a result, the gate voltages of the PMOS FETsM_(11′) (327) through M_(1N) (328) in the first FET stack (325) areapproximately the same as the voltage V₁ (372).

The drain voltage of the PMOS FET M_(1N) (328) is the voltage V_(R1-max)(375 a), and the gate voltage of each PMOS FET M₁₁ (327) through M_(1N)(328) is approximately the intermediate voltage V₁ (372). Consequently,the PMOS FETs M₁₁ (327) through M_(1N) (328) are operating in triodemode since V_(DG)≈V_(R1-max)−V₁>|V_(TP)| for each of the PMOS FETs inthe first FET stack (325). Accordingly, the state of any of the FETs atany instant of time, that is whether they are biased off or saturated inthe on mode or operating in the triode mode is dependent upon themagnitude and polarity of the source, drain and gate voltages of eachdevice. The triode mode is understood by those skilled in the art todenote the linear region of operation for the device.

The source-to-gate voltage V_(SG) of PMOS FET M₁₀ (305) is equal toV_(DD)−(V₁+|V_(TP)═), which is sufficiently large such that PMOS FET M₁₀(305) is operating in the triode mode. As a result, the voltage V_(R1)(375) supplies current from the first node N_(R1) (376) through the PMOSFETs M_(1N) (328) through M₁₀ (305) to the output node N_(OUT) (390).Aside from the small voltage drops due to the on-resistance of the PMOSFETs M_(1N) (328) through M₁₀ (305), the maximum value V_(R1-max) (375a) of the voltage V_(R1) (375) is essentially tied to the DC outputvoltage V_(DD) (395).

Since V_(R1) is greater than the ground potential, the diode D_(NS1)(315) is reverse biased. Also, the minimum value for the voltage V_(R2)(380), denoted as V_(R2-min) (380 a), is at least one diode drop V_(NSD)below the ground terminal (392). Consequently, the diode D_(NS2) (320)is forward biased and the voltage V_(R2) (380) supplies current from thenode N_(R2) (381) to the ground terminal (392).

The diode connected BJT D₂ (355) is forward biased whenV_(R2)<V₁−V_(D2), where V_(D2) is a diode voltage drop of the BJT D₂(355). The small value for the voltage V_(R2-min) (380 a) drives thediode connected BJT D₂ (370) to be forward biased. Consequently, currentflows from the output node N_(OUT) (390) through the diode connectedPMOS FETs M_(B1) (360) through M_(B3) (364) to the intermediate node A(373). The current then flows from the intermediate node A (373) throughthe second resistor ladder (345) to intermediate node B (374). Thecurrent flows from the intermediate node B (374) through the diodeconnected BJT D₂ (355) and through the diode D_(NS2) (320) to groundterminal (392).

Since the diode connected BJT D₂ (355) is forward biased, current flowsthrough the second resistor ladder (345) and the gate voltage V_(G2k) ofa k-th PMOS FET M_(2k) (334) in the second FET stack (330) can beexpressed as the following equation:

$V_{G\; 2k} = {\frac{\left\lbrack {V_{1} - \left( {V_{R\; 2} + V_{D\; 2}} \right)} \right\rbrack{\sum\limits_{i = k}^{N}R_{2i}}}{\sum\limits_{j = 1}^{N}R_{2j}} + V_{R\; 2} + V_{D\; 2}}$where V₁−(V_(R2)+V_(D2)) is the voltage difference between theintermediate node A (373) and the intermediate node B (374), where

Σ_(i=k) ^(N)R_(2i) is the total resistance of resistors R_(2k) throughR_(2N), and

Σ_(j=1) ^(N)R_(2j) is the total resistance of the second resistor ladder(345).

As a result, high voltage difference between the output voltage V_(DD)(395) and the voltage V_(R2) (380) will be shared between the PMOS FETsM₂₀ (310) through M_(2N) (333). Since the drain voltage of PMOS FET M₁₀(305), denoted as V_(d)(M₁₀), has a value close to the output voltageV_(DD) (395), the gate-to-source voltage of PMOS FET M₂₀ (310), denotedas V_(GS)(M₂₀), is given by V_(GS)(M₂₀)=V_(DD)−V_(D)(M₁₀)≈0. The PMOSFET M₂₀ (310) operates in the cutoff region since the conditionV_(GS)(M₂₀)>V_(TP) is satisfied. Consequently, negligible current flowsthrough PMOS M₂₀ (310) as well as the PMOS FETs M₂₁ (332) through M_(2N)(333) in the second FET stack (330). As a result, the source-to-gatevoltage of a k-th PMOS FET M_(2k) (334), denoted as V_(SG2k), isapproximately equal to |V_(TP)|.

The second FET stack (330) is adapted to withstand a large voltagedifference between the output voltage V_(DD) (395) to the voltage V_(R2)(380) to prevent the PMOS FETs M₂₀ (310) through M_(2N) (333) fromoperating under stress conditions. Stress conditions are understood tobe operation of MOSFETs at voltages greater than their breakdown voltageand that the MOSFETs will be functioning with terminal voltages beyondtheir optimum or recommended terminal voltage difference limits. Inorder to prevent PMOS FETs M₂₁ (332) through M_(2N-1) from operatingunder stress conditions, voltage across each resistor R₂₁ throughR_(2N-1) is less than the smaller of BV{GD_(2k)}+|V_(TP)| andBV{SD_(2k)}, where BV{GD_(2k)} and BV{SD_(2k)} are the gate to drainbreakdown voltage and the source to drain breakdown voltage,respectively, of the k-th PMOS FET in the second FET stack (333), wherek is a value between 1 through N-1. Additionally, to avoid operatingunder stress conditions, the gate to drain breakdown voltage of the lastPMOS FET M_(2N) (333) in the second FET stack (330), denoted asBV{GD_(2N)}, is greater than V_(R2N)+V_(D2), where V_(R2N) is thevoltage across the last resistor R_(2N) (348) of the second resistorladder (345).

To obtain a maximum value for the DC output voltage V_(DD) (395), whichis limited by the diode breakdown voltage of the NWell/substrate diodesfor PMOS FET M₂₀ (310), denoted as BV{NSD}, the number of PMOS FETs inthe second FET stack (330) is given by the following equation:

$N = \left\lceil {\frac{{BV}\left\{ {NSD} \right\}}{\min\left\lbrack {{{{BV}\left\{ {GD}_{2k} \right\}} + {V_{TP}}},{{BV}\left\{ {SD}_{2k} \right\}}} \right\rbrack} - 1} \right\rceil$For an exemplary 0.18 um CMOS process, N is equal to 3 and 6 for 3.3 Vinput/output PMOS FETs and 1.8 V normal PMOS FETs (with 2 V maximumlimits), respectively. Typically, the breakdown voltage for the 3.3 VPMOS is about 3.6 V. As will be discussed later in more detail for theVoltage Doubler circuit of FIG. 5, the individual diodes D_(NS1) (315)and D_(NS2) (320) may be replaced by and are functionally equivalent to“active diodes” which are circuits, comprising a MOSFET and acomparator, that provides unidirectional current flow when the output ofthe comparator causes the MOSFET to be forward biased, A characteristicof active diodes is that there is essentially no voltage drop across theactive diode when the MOSFET is forward biased.Case b: V_(R1)≧V_(R2), V_(2P)>V_(R1)−V_(R2)≧0

For the second case b (405) when the induced voltage V₂ (370) begins todrop from the peak value V_(2P) (370 a). The drain voltage of PMOS FETM₁₀ (305) and the voltage V_(R1) (375) remain essentially tied to theoutput voltage V_(DD) (395) since the PMOS FET M₁₀ (305) continues tooperate in the triode region.

However, since the value of the voltage V_(R2) (380) is increasing incase b (405), the diode D_(NS2) (320) is reverse biased and no currentflows from the output node N_(OUT) (390) to the ground terminal (392).Note that both diode D_(NS1) (315) and diode D_(NS2) (320) are reversebiased. Therefore, current flows only from the output node N_(OUT) (390)to node N_(R2) (381) by flowing through the diode connected PMOS FETsM_(B1) (360) through M_(B3) (364), the second resistor ladder (345), andthe diode connected BJT D₂ (355), keeping intermediate voltage V₁ (372)relatively constant.

Case c: V_(R1)<V_(R2), |V_(2P)|≧|V_(R1)−V_(R2)|

Finally, for the third case c (410) when the induced voltage V₂ (370)becomes negative and continues to decrease. As the voltage V_(R2) (380)increases, the gate voltage applied to PMOS FET M₁₀ (305) is notsufficiently large as to tie the voltage V_(R1) (375) to the output nodeN_(OUT) (390) and the voltage V_(R1) (375) begins to decrease. The PMOSFET M₁₀ (305) enters cutoff mode when V_(R1)<V_(DD)−|V_(TP)|.

When the voltage V_(R2) (380) further increases to a value larger thanV₁-V_(D2), the diode connected BJT D₂ (320) begins to operate in reversebias. As a result, no significant current flows through the resistorsR₂₁ through R_(2N) in the second resistor ladder (345).

The status of each transistor, at this point, is given as follows: thediode connected BJT D₁ (350) is reverse biased, the diode connected BJTD₁ (355) is reverse biased, the PMOS FETs M₁₀ (305) through M_(1N) (328)are operating in the cutoff mode, and the PMOS FETs M₂₀ (310) throughM_(2N) (333) are operating in the cutoff mode, and the diode connectedPMOS FETs M_(B1) (360) through M_(B3) (364) are operating in the cutoffmode. The intermediate voltage V₁ (372) may increase to aboutV_(DD)−3|V_(TP)| and remain at the voltage V_(DD)−3|V_(TP)| due to thecharge stored on a capacitor C_(P) (366).

As the voltage V_(R1) (375) decreases further and reaches one diode dropV_(NSD) below the ground terminal (392), the diode D_(NS1) (315) becomesforward biased. Consequently, current flows from node N_(R1) (376) tothe ground terminal (392). On the other hand, as the voltage V_(R2)(380) increases further, the PMOS FETs M₂₀ (310) through M_(2N) (333)begin to operate in the triode mode. The node N_(R2) (381) becomes tiedto the output node N_(OUT) (390), and thus current flows from the nodeN_(R2) (381) to the output node N_(OUT) (390).

The gate voltages V_(G2k) are approximately equal to the intermediatevoltage V₁ (372) since negligible current flows through the secondresistor ladder (345). At this instance, the PMOS FETs M_(B1) throughM_(B3) are in a saturation mode and conducting current through theresistor ladder (340). The PMOS FETs in the second PMOS stack (330),namely PMOS FETs M₂₁ (332) through M_(2N) (333) operate in triode modeand will remain in triode mode until the induced voltage V₂ (370)becomes positive. Consequently, the voltage V_(R2) (380) suppliescurrent from the node N_(R2) (381) flows to the output node N_(OUT)(390) through transistors M_(2N) (333) and M₂₀ (310) until the inducedvoltage V₂ (370) becomes positive.

When the induced voltage V₂ (370) reaches its negative peak −V_(2P) incase c (410), the operation of the left and right circuit branches shownin FIG. 3 are reversed in relation to case a (400). The operations willreverse again between the beginning of a fourth case d (415) and the endof the fourth case d (415).

The DC output voltage V_(DD) (395) is approximated by the followingequation:V _(DD) ≈|V _(R1) −V _(R2)|_(peak)−(N+1)V _(SD) −V _(NSD)where, for simplicity, the source to drain voltage of each of the PMOSFETs M₁₀ (305) through M_(1N) (328) as well as M₂₀ (310) through M_(2N)(333) are assumed to be equal and denoted as V_(SD). From the aboveequation, it can be seen that the output voltage V_(DD) (395) is atleast about 0.7 V, corresponding to the forward diode drop V_(NSD),lower than the peak induced voltage V_(2P) (370 a). Additionally, theoutput voltage V_(DD) (395) can be maximized by increasing the PMOS FETwidths, which reduces the value of V_(SD). Additionally, the V₂ (370)curve as shown in FIG. 4, has a peak to peak value of about 28 V at afrequency of 100 kHz.

Although the foregoing circuit description has been undertaken utilizingPMOS FET devices, as mentioned previously, it is to be understood that acomplementary circuit for a high voltage full wave rectifier may beimplemented utilizing NMOS FET devices taking into account thecorresponding appropriate voltage polarities for proper circuitoperation as understood by one skilled in the art.

HV Voltage Doubler Design

By way of background and with reference to FIG. 1, to acquire a largevalue for the induced voltage V₂ (115), the coil L (120) requires morewindings, which generally results in an increase in the physical size ofthe coil L (120). Such an increase in the physical size of the coil L(120) may not be desirable for small biomedical implantable devices.However, if a voltage doubler is employed, a certain required DC outputvoltage V_(DC) (130) can be obtained with peak to peak value of theinduced voltage V₂ (115) reduced by half.

In discrete implementations, a voltage doubler generally utilizes twodiodes. Both a positive supply rail V_(DD) and a negative supply railV_(SS) are provided. An NWell/p-substrate diode can be used to supplythe negative supply current. An overall voltage doubler outputV_(DD)−V_(SS) is equal to the peak to peak value of the induced voltageminus two diode drops. However, in order to maximize the voltage doublercircuit output, transistors with active control circuits may be used torealize the two required diodes to minimize the overall voltage drops.

FIG. 5 shows an exemplary embodiment of a high voltage (HV) voltagedoubler (500). The HV voltage doubler (500) is adapted for use with aninduced voltage V₂ (505). The voltage doubler (500) generates a positivesupply voltage V_(DD) (510) and a negative supply voltage V_(SS) (515).An overall DC output voltage V_(Doub) (520) is given byV_(Doub)=V_(DD)−V_(SS). With V_(SS) having a negative potential and amagnitude equal to V_(DD), the output of the doubler circuit will betwice the value of V_(DD). To maximize the output voltage V_(Doub)(520), the two diodes generally used in voltage doublers are replaced bytransistors with active control circuits. In particular, the transistorsare M_(P0) (525) and M_(N0) (530) and the active control circuits are afirst comparator A_(P) (550) and a second comparator A_(N) (560)respectively.

High voltage operations are achieved by connecting in series circuitarrangement a PMOS FET stack (526) to PMOS FET M_(P0) (525), wherein thePMOS FET stack (526) comprises PMOS FETs M_(P1) through M_(PN), and byconnecting in series circuit arrangement a NMOS FET stack (530) to NMOSFET M_(N0) (531), wherein the NMOS FET stack (530) comprises NMOS FETsM_(NN) through M_(N1). The PMOS FETsM_(P0) (525) through M_(PN) areconnected drain-to-source in series circuit arrangement. The NMOS FETsM_(NN) through M_(N0) (530) are connected source to drain in seriescircuit arrangement. A first resistor ladder (528), comprising resistorsR_(P1) through R_(PN), is connected with the PMOS FET stack (526). Theresistor R_(PN) in the first resistor ladder (528) is connected inseries with a diode connected BJT Q_(P) (535). A second resistor ladder(533), comprising resistors R_(N1) through R_(NN), is connected with theNMOS FET stack (531). The resistor R_(NN) in the second resistor ladder(533) is connected in series with a diode connected BJT Q_(N) (540). TheNMOS FETs are isolated from the p-substrate using the DNWell option suchthat their bulk terminals are connected to their corresponding sourceterminals.

The voltage doubler (500) further comprises the first comparator A_(P)(550) and second comparator A_(N) (560). The first comparator A_(P)(550) includes a (positive) input terminal (552) a (negative) inputterminal (553) and an output terminal N_(AP) (554). The positive voltagesupply V_(DD) (510) is applied to input terminal (552) of the firstcomparator A_(P) (550) while a drain voltage V_(DP0) (545) of PMOS FETM_(P0) (525) is applied to input terminal (553).

Similarly, the second comparator A_(N) (560) includes a (positive) inputterminal (562) a (negative) input terminal (563) and an output terminalN_(AN) (564). The negative voltage supply V_(SS) (515) is applied toinput terminal (563) while a source voltage V_(SN0) (570) of NMOS FETM_(N0) (530) is applied to input terminal (562).

Referring now to both FIGS. 5 and 6, FIG. 6 shows voltage waveforms forthe HV voltage doubler (500) shown in FIG. 5. In particular, FIG. 6shows, as a function of time, the induced voltage V₂ (505), the positivevoltage supply V_(DD) (255), and the negative voltage supply V_(SS)(510). Specifically, a first case a (600) and second case b (605) willbe described in detail below.

Case a: V₂>V_(DD)

For case a (600) when the induced voltage V₂ (505) increases toward itspositive peak value and becomes larger than the output voltage V_(DD)(510) the large value of V₂ (505) drives the PMOS FETs M_(P1) throughM_(PN) in the PMOS FET stack (526) into the triode mode. Additionally,the diode connected BJT Q_(P) (535) reverse biased and thus does notconduct any significant current and consequently, no current flowsthrough the resistors in a first resistor ladder (528). With no voltagedrop across the resistors in the first resistor ladder (528), the gatevoltage of each PMOS FET in the PMOS FET stack (526) is about equal to avoltage V_(P1) (575). Since resistance of each PMOS FET is negligible,most of the induced voltage V₂ (505) appears as drain voltage V_(DP0)(545) and at comparator A_(P) (550) input terminal (553).

When comparator A_(P) (550) detects that the drain voltage V_(DP0) (545)is higher than the output voltage V_(DD) (510) by a small offset voltageV_(POS) (not shown) set in the comparator A_(P) (550), the gate voltageapplied to PMOS FET M_(P0) (525) is driven to a value lower than V_(DD)so as to turn on PMOS FET M_(P0) (525). Since PMOS FET M_(P0) (525) andthe PMOS FETs in the PMOS FET stack (526) are turned on, current flowsfrom node N_(IN) (506) to output node N_(OUT-DD) (511).

A small offset voltage V_(POS) (not shown) may be used to compensate forcomparator A_(P) (550) delay in turning the PMOS FET M_(P0) (525) off.Use of voltage offsets for such compensation is shown in “AnEfficiency-Enhanced Integrated CMOS Rectifier with Comparator-ControlledSwitches for Transcutaneous Powered Implants,” by S. Guo and H. Lee,Proc. IEEE 2007 CICC, pp. 385-388, September 2007, which is incorporatedherein by reference in its entirety.

Conversely, the source voltage V_(SN0) (570) at NMOS FET M_(N0) (530) ishigher than V_(SS) (515) and is given as V_(N1)-V_(TN.), Therefore, theoutput of the second comparator A_(N) (560) is at a value of V_(SS)(515) (i.e. logic 0) to cause the NMOS FET M_(N0) (530) to be turnedoff. Since the NMOS FET M_(N0) (530) is turned off, no current flowsfrom put node N_(IN) (506) to node N_(OUT-SS) (516).

At such time, the diode connected BJT Q_(N) (540) is forward biasedbecause of the large value of the induced voltage V₂ (505). Sincecurrent flows through the second resistor ladder (533) the gate voltagesof the NMOSs M_(N1) through M_(NN) are set by the voltage dividercomprising the BJT Q_(N) (540) and the resistors R_(N1) through R_(NN).Therefore, the NMOS FETs in the NMOS FET stack (531) will not be understress conditions so long as breakdown voltages are not reached

When the induced voltage V₂ (505) and thus the drain voltage V_(DP0)(545), decreases below a threshold V_(DD)+V_(POS), the comparator A_(P)(550) output node N_(AP) (554) is driven to a value equal to V_(DD) andthe PMOS FET M_(P0) (525) is turned off. Once the PMOS FET M_(P0) (525)turns off, current cannot flow from the output node N_(OUT-DD) (511) tothe input node N_(IN) (506). The voltage offset V_(POS) of thecomparator A_(P) (not shown) is added in order to minimize currentflowing from the output node N_(OUT-DD) (511) to the input node N_(IN)(506) due to delay of the comparator A_(P) (550) in turning off the PMOSFET M_(P0) (525). By adding the voltage offset V_(POS), the comparatorA_(P) (550) turns off the PMOS FET M_(P0) (525) slightly earlier thanthe comparator A_(P) (550) would have turned off the PMOS FET M_(P0)(525) had there been no voltage offset V_(POS) in order to compensatefor the delay.

Consequently, the positive voltage supply V_(DD) (510) is tied to aconstant value since only negligible current flows from the output nodeN_(OUT-DD) (511) to the input node RN (506). The positive voltage supplyV_(DD) (510) will be tied to this constant value until the end of a timeperiod c (610), when the operations in case a (600) will repeat.

Case b: V₂<V_(SS)

For the second case b (605) where the induced voltage V₂ (505) is in thevicinity of its negative peak value −V_(2P). The diode connected BJTQ_(N) (540) is reverse biased and thus no current flows through thesecond resistor ladder (533). The NMOS FETs M_(NN) through M_(N1) in theNMOS FET stack (531) operate in the triode mode with their gate voltagesequal to a voltage V_(N1) (580). Since resistance across each NMOS FETis negligible, most of the induced voltage V₂ (505) appears as a sourcevoltage V_(SN0) (570) of NMOS FET M_(N0) (530).

When the induced voltage v₂ (505) is near its negative peak, the outputof comparator A_(N) (560) will be higher than V_(SS) so as to turn onthe NMOS FET M_(N0) (530). Consequently, current flows from the inputnode N_(IN) (506) to the output node N_(OUT-SS) (516). Similar to thecase for the first comparator A_(P) (550), the second comparator A_(N)(560) also has a voltage offset V_(NOS) (not shown) that compensates fordelay of the comparator A_(N) (560) in turning off the NMOS FET M_(N0)(530) when the induced voltage V₂ (505) increases above V_(SS)−V_(NOS).

The negative voltage supply V_(SS) (515) remains at a constant valuesince only negligible current flows from the output node N_(OUT-SS)(516) to the input node N_(IN) (506). The negative voltage supply V_(SS)(515) will be tied to this constant value until the end of a time periodd (615), upon which the operations in case b (605) will repeat.

A resistor R₁ (590) and a resistor R₂ (591) are used to ensure that someDC biasing currents exist for both the first comparator A_(P) (550) andthe second comparator A_(N) (560) and the capacitors C₁ and C₂ connectedin parallel with resistors R₁ (590) and R₂ (591) respectively, providerelatively constant supply voltages for the comparators A_(P) (550) andA_(N) (560). Additionally, capacitor C₄ (512) coupled between outputnode N_(OUT-DD) (511) (V_(DD)) and ground and capacitor C₅ (513) coupledbetween output node N_(OUT-SS) (516) (V_(SS)) and ground function asfilter capacitors for signal smoothing.

Since both the positive voltage supply V_(DD) (510) and the negativevoltage supply V_(SS) (515) are tied to their respective constantvalues, the voltage doubler voltage output V_(Doub) (520), given byV_(Doub)=V_(DD)−V_(SS), is also substantially a constant value.

FIG. 7 shows an exemplary embodiment of the comparator A_(P) (550). Adiode connected PMOS FET M_(BP1) (700), a diode connected PMOS FETM_(BP2) (705), and a diode connected PMOS FET M_(BP3) (710) are used forestablishing supply rails. The supply rails are the voltages V_(DD)(510) and V_(P1) (575), as shown in FIG. 5. The capacitor C_(P) servesto ensure that the voltage between V_(DD) and V_(P1) is relativelyconstant. A voltage difference between the voltage V_(DD) (510) at thefirst terminal (552) of the comparator A_(P) (550) and the voltageV_(P1) (540) is set at 3V_(SG) due to voltage drops of each of the diodeconnected PMOS FETs (700, 705, 710). In the current, exemplaryembodiment a typical value for V_(SG) is about 1 volt. The diodeconnected PMOSs (700, 705, 710) are also used for generating a biascurrent for the comparator core (715) comprising PMOS FETs M₁ throughM₄. An output from the comparator core (715) is further amplified byPMOS FETs M₇ and M₈. Since the comparator A_(P) (550) is supplied with avoltage of V_(DD)−V_(P1), the gate voltage swing of the PMOS FET M_(P0)(525) in FIG. 5 is limited to about 3V_(SG). The offset V_(POS) isobtained by adjusting the width-to-length ratio of the PMOS FETs M₁ andM₂ as well as the currents on PMOS FETs M₃ and M₄.

The design of the second comparator A_(N) (560) is similar to the designof the first comparator A_(P) (550) except that all PMOS FETs in thecomparator A_(P) (550) are replaced with NMOS FETs and all NMOS FETs inthe comparator A_(P) (550) are replaced with PMOS FETs.

Specifically, in practice the voltage waveforms shown in FIG. 6illustrate example numerical results for the circuit shown in FIG. 5.For such example, the voltage doubler (500) was set to have an outputpower P_(out) of 8.85 mW. The induced voltage V₂ (505) has a peak topeak value of 13.93 V and a frequency of 100 kHz. The value for thepositive supply V_(DD) (510) is about 6.7 V and the value for thenegative supply V_(SS) (515) is about −6.6 V. The resulting voltagedoubler output voltage V_(Doub) (520) is V_(Doub)=V_(DD)−V_(SS)=13.3 V.

With reference to FIGS. 5 and 6, the HV voltage doubler (500) requiredthe induced voltage V₂ (505) to have a peak to peak value of around 14 Vin order to generate the voltage doubler DC output V_(Doub) (520) ofaround 13.3 V. With reference to FIGS. 3 and 4, the high voltage fullwave rectifier (300) required the induced voltage V₂ (370), shown inFIG. 3, to have a peak to peak value of around 28 V in order to generatethe rectifier DC output V_(DD) (510) of around 13.3 V.

A number of embodiments of the disclosure have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the presentdisclosure. Accordingly, other embodiments are within the scope of thefollowing claims.

What is claimed is:
 1. A high voltage full wave rectifier implementedutilizing low voltage CMOS process transistors, said rectifier having anoutput terminal, a ground terminal and a pair of input terminals, saidinput terminals coupled to a time varying voltage signal, the rectifiercomprising: a pair of mosfet transistors connected together in a crosscoupled circuit arrangement, the source of each transistor coupled tothe output terminal; a first plurality of mosfet transistors coupledtogether in a stacked series circuit arrangement, the source of thefirst mosfet in such series being coupled to the drain of one of themosfet transistors in the cross coupled arrangement, the drain of thelast mosfet in the series coupled to one input terminal; a firstplurality of resistors interconnected in series circuit arrangement,said first plurality of resistors coupled between the output terminaland one input terminal, wherein the gates of the first plurality ofmosfet transistors are coupled to respective ones of theinterconnections of the first plurality of resistors for controlling thestate of the respective mosfet transistors coupled thereto; a secondplurality of mosfet transistors coupled together in a stacked seriescircuit arrangement, the source of the first mosfet in such series beingcoupled to the drain of the other one of the mosfet transistors in thecross coupled arrangement, the drain of the last mosfet in the seriescoupled to the other one of the input terminals; a second plurality ofresistors interconnected in series circuit arrangement, said secondplurality of resistors coupled between the output terminal and the otherone of the input terminals, wherein the gates of the second plurality ofmosfet transistors are coupled to respective ones of theinterconnections of the second plurality of resistors for controllingthe state of the respective mosfet transistors coupled thereto; and afirst diode coupled between one input terminal and ground and a seconddiode coupled between the other input terminal and ground.
 2. Therectifier of claim 1 wherein the connection between the first pluralityof resistors and the output terminal includes, in series circuitarrangement, at least one semiconductor device configured to function asa diode and wherein the connection between the second plurality ofresistors and the output terminal includes, in series circuitarrangement, such at least one semiconductor device configured tofunction as a diode.
 3. The rectifier of claim 2 wherein the at leastone semiconductor device comprises at least one mosfet transistor. 4.The rectifier of claim 3 wherein the mosfet transistors comprise PMOSFETs.
 5. The rectifier of claim 1 wherein the connection between thefirst plurality of resistors and said one input terminal includes, inseries circuit arrangement, at least one semiconductor device configuredto function as a diode and wherein the connection between the secondplurality of resistors and said other one of the input terminalincludes, in series circuit arrangement, such at least one semiconductordevice configured to function as a diode.
 6. The rectifier of claim 1further comprising a capacitor connected between the output terminal andthe first and second plurality of resistors.
 7. The rectifier of claim 1wherein the mosfet transistors comprise PMOS FETs.
 8. The rectifier ofclaim 1 wherein the first and second diodes are active diodes.
 9. Therectifier of claim 1 wherein the resistance values of the resistors inthe first and second plurality of resistors are selected to maintainoperation of the first and second plurality of mosfet transistorsrespectively below their breakdown voltage.
 10. The rectifier of claim 1wherein the resistance values of the resistors in the first and secondplurality of resistors are selected to maintain operation of the firstand second plurality of mosfet transistors respectively such that thedrain to source voltage of each transistor in the first and secondplurality of mosfet transistors are equal.
 11. A full wave rectifierimplemented utilizing low voltage CMOS process transistors, saidrectifier having an output terminal, a ground terminal and first andsecond input terminals, said input terminals coupled to a time varyingvoltage signal, the rectifier comprising: first and second mosfettransistors connected together in a cross coupled circuit arrangement,each transistor being coupled to the output terminal; a first stack oflow voltage CMOS process transistors, the first transistor in such stackbeing coupled to the first transistor in the cross coupled arrangement,the last transistor in such stack being coupled to the first inputterminal; a first plurality of resistors interconnected in seriescircuit arrangement, said first plurality of resistors coupled betweenthe output terminal and the first input terminal, wherein the gates ofthe transistors in the first stack are coupled to respective ones of theinterconnections of the first plurality of resistors for controlling thestate of the respective transistors coupled thereto; a second stack oflow voltage CMOS process transistors the first transistor in such stackbeing coupled to the second transistor in the cross coupled arrangement,the last transistor in such stack coupled to the second input terminal;a second plurality of resistors interconnected in series circuitarrangement, said second plurality of resistors coupled between theoutput terminal and the second input terminal, wherein the gates of thetransistors in the second stack are coupled to respective ones of theinterconnections of the second plurality of resistors for controllingthe state of the respective transistors coupled thereto; and a firstdiode coupled between the first input terminal and ground and a seconddiode coupled between the second input terminal and ground.
 12. Therectifier of claim 11 wherein the connection between the first pluralityof resistors and the output terminal includes, in series circuitarrangement, at least one semiconductor device configured to function asa diode and wherein the connection between the second plurality ofresistors and the output terminal includes, in series circuitarrangement, such at least one semiconductor device configured tofunction as a diode.
 13. The rectifier of claim 12 wherein the at leastone semiconductor device comprises a plurality of semiconductor devicesand wherein the magnitude of a bias voltage established across the firstplurality of resistors and ground is a function of the number of devicescontained within such plurality of semiconductor devices.
 14. Therectifier of claim 11 wherein the connection between the first pluralityof resistors and said first input terminal includes, in series circuitarrangement, at least one semiconductor device configured to function asa diode and wherein the connection between the second plurality ofresistors and said second input terminal includes, in series circuitarrangement, such at least one semiconductor device configured tofunction as a diode.
 15. The rectifier of claim 11 wherein the first andsecond diodes are active diodes.
 16. The rectifier of claim 11 whereinthe resistance values of the resistors in the first and second pluralityof resistors are selected to maintain operation of the transistors inthe first and second stack of transistors respectively, below theirbreakdown voltage.
 17. The rectifier of claim 11 wherein the resistancevalues of the resistors in the first and second plurality of resistorsare selected to maintain operation of the transistors in the first andsecond stack of transistors, respectively, such that the drain to sourcevoltage of each transistor in the first and second stack of transistorsare equal.